Geology topics

David M. Sumner

Publications and source records attributed to David M. Sumner.

8 recordsLinked to original sources

USGS2018

A simple method for partitioning total solar radiation into diffuse/direct components in the United States

Solar radiation is a major sustainable and clean energy resource, and use of solar radiation is expected to increase. The utilization efficiency of solar energy varies with the relative proportions of the direct and diffuse components that compose total solar radiation and with the slope and aspect of the irradiated surface. The purpose of this paper is to develop a simple method for estimating diffuse and direct solar radiation at sites with observation of only total solar radiation. An existing model for estimating diffuse radiation, i.e., a linear relationship between the diffuse fraction (the ratio of diffuse radiation to total solar radiation) and the clearness index (the ratio of total solar radiation to extraterrestrial radiation), is applied to 7 sites across the continental United States with observations of diffuse and total radiation. The linear model shows good monthly performance. The model parameters (slope and interception) show a strong seasonal pattern that exhibits small variation across the 7 sites; therefore, the average values of the two monthly parameters may be used for estimating diffuse radiation for other locations with observations of total radiation.

International Journal of Green Energy↗

USGS2017

Estimating belowground carbon stocks in isolated wetlands of the Northern Everglades Watershed, central Florida, using ground penetrating radar (GPR) and aerial imagery

Peat soils store a large fraction of the global soil carbon (C) pool and comprise 95% of wetland C stocks. While isolated freshwater wetlands in temperate and tropical biomes account for more than 20% of the global peatland C stock, most studies of wetland soil C have occurred in expansive peatlands in northern boreal and subarctic biomes. Furthermore, the contribution of small depressional wetlands in comparison to larger wetland systems in these environments is very uncertain. Given the fact that these wetlands are numerous and variable in terms of their internal geometry, innovative methods are needed for properly estimating belowground C stocks and their overall C contribution to the landscape. In this study, we use a combination of ground penetrating radar (GPR), aerial imagery, and direct measurements (coring) in conjunction with C core analysis to develop a relation between C stock and surface area, and estimate the contribution of subtropical depressional wetlands to the total C stock of pine flatwoods at the Disney Wilderness Preserve (DWP), Florida. Additionally, GPR surveys were able to image collapse structures underneath the peat basin of depressional wetlands, depicting lithological controls on the formation of depressional wetlands at the DWP. Results indicate the importance of depressional wetlands as critical contributors to the landscape C budget at the DWP and the potential of GPR-based approaches for (1) rapidly and noninvasively estimating the contribution of depressional wetlands to regional C stocks and (2) evaluating the formational processes of depressional wetlands.

Florida↗

USGS2017

Use of eddy-covariance methods to "calibrate" simple estimators of evapotranspiration

Direct measurement of actual evapotranspiration (ET) provides quantification of this large component of the hydrologic budget, but typically requires long periods of record and large instrumentation and labor costs. Simple surrogate methods of estimating ET, if â€œcalibratedâ€ to direct measurements of ET, provide a reliable means to quantify ET. Eddy-covariance measurements of ET were made for 12 years (2004-2015) at an unimproved bahiagrass (Paspalum notatum) pasture in Florida. These measurements were compared to annual rainfall derived from rain gage data and monthly potential ET (PET) obtained from a long-term (since 1995) U.S. Geological Survey (USGS) statewide, 2-kilometer, daily PET product. The annual proportion of ET to rainfall indicates a strong correlation (r 2 =0.86) to annual rainfall; the ratio increases linearly with decreasing rainfall. Monthly ET rates correlated closely (r 2 =0.84) to the USGS PET product. The results indicate that simple surrogate methods of estimating actual ET show positive potential in the humid Florida climate given the ready availability of historical rainfall and PET.

Conference Paper↗

USGS2013

A comparison of models for estimating potential evapotranspiration for Florida land cover types

We analyzed observed daily evapotranspiration (DET) at 18 sites having measured DET and ancillary climate data and then used these data to compare the performance of three common methods for estimating potential evapotranspiration (PET): the Turc method (Tc), the Priestley-Taylor method (PT) and the Penman-Monteith method (PM). The sites were distributed throughout the State of Florida and represent a variety of land cover types: open water (3), marshland (4), grassland/pasture (4), citrus (2) and forest (5). Not surprisingly, the highest DET values occurred at the open water sites, ranging from an average of 3.3 mm d -1 in the winter to 5.3 mm d -1 in the spring. DET at the marsh sites was also high, ranging from 2.7 mm d -1 in winter to 4.4 mm d -1 in summer. The lowest DET occurred in the winter and fall seasons at the grass sites (1.3 mm d -1 and 2.0 mm d -1 , respectively) and at the forested sites (1.8 mm d -1 and 2.3 mm d -1 , respectively). The performance of the three methods when applied to conditions close to PET (Bowen ratio ≤ 1) was used to judge relative merit. Under such PET conditions, annually aggregated Tc and PT methods perform comparably and outperform the PM method, possibly due to the sensitivity of the PM method to the limited transferability of previously determined model parameters. At a daily scale, the PT performance appears to be superior to the other two methods for estimating PET for a variety of land covers in Florida.

Florida↗

USGS2012

Measurement and simulation of evapotranspiration at a wetland site in the New Jersey Pinelands

Evapotranspiration (ET) was monitored above a wetland forest canopy dominated by pitch-pine in the New Jersey Pinelands during November 10, 2004-February 20, 2007, using an eddy-covariance method. Twelve-month ET totals ranged from 786 to 821 millimeters (mm). Minimum and maximum ET rates occurred during December-February and in July, respectively. Relations between ET and several environmental variables (incoming solar radiation, air temperature, relative humidity, soil moisture, and net radiation) were explored. Net radiation (r = 0.72) and air temperature (r = 0.73) were the dominant explanatory variables for daily ET. Air temperature was the dominant control on evaporative fraction with relatively more radiant energy used for ET at higher temperatures. Soil moisture was shown to limit ET during extended dry periods. With volumetric soil moisture below a threshold of about 0.15, the evaporative fraction decreased until rain ended the dry period, and the evaporative fraction sharply recovered. A modified Hargreaves ET model, requiring only easily obtainable daily temperature data, was shown to be effective at simulating measured ET values and has the potential for estimating historical or real-time ET at the wetland site. The average annual ET measured at the wetland site during 2005-06 (801 mm/yr) is about 32 percent higher than previously reported ET for three nearby upland sites during 2005-09. Periodic disturbance by fire and insect defoliation at the upland sites reduced ET. When only undisturbed periods were considered, the wetland ET was 17 percent higher than the undisturbed upland ET. Interannual variability in wetlands ET may be lower than that of uplands ET because the upland stands are more susceptible to periodic drought conditions, disturbance by fire, and insect defoliation. Precipitation during the study period at the nearby Indian Mills weather station was slightly higher than the long-term (1902-2011) annual mean of 1,173 millimeters (mm), with 1,325 and 1,396 mm of precipitation in 2005 and 2006, respectively.

New Jersey↗

USGS2011

Variability of albedo and utility of the MODIS albedo product in forested wetlands

Albedo was monitored over a two-year period (beginning April 2008) at three forested wetland sites in Florida, USA using up- and down-ward facing pyranometers. Water level, above and below land surface, is the primary control on the temporal variability of daily albedo. Relatively low reflectivity of water accounts for the observed reductions in albedo with increased inundation of the forest floor. Enhanced canopy shading of the forest floor was responsible for lower sensitivity of albedo to water level at the most dense forest site. At one site, the most dramatic reduction in daily albedo was observed during the inundation of a highly-reflective, calcareous periphyton-covered land surface. Satellite-based Moderate-Resolution Imaging Spectroradiometer (MODIS) estimates of albedo compare favorably with measured albedo. Use of MODIS albedo values in net radiation computations introduced a root mean squared error of less than 4.7 W/m 2 and a mean, annual bias of less than 2.3 W/m 2 (1.7%). These results suggest that MODIS-estimated albedo values can reliably be used to capture areal and temporal variations in albedo that are important to the surface energy balance.

Florida↗

USGS2005

Estimating changes in heat energy stored within a column of wetland surface water and factors controlling their importance in the surface energy budget

Changes in heat energy stored within a column of wetland surface water can be a considerable component of the surface energy budget, an attribute that is demonstrated by comparing changes in stored heat energy to net radiation at seven sites in the wetland areas of southern Florida, including the Everglades. The magnitude of changes in stored heat energy approached the magnitude of net radiation more often during the winter dry season than during the summer wet season. Furthermore, the magnitude of changes in stored heat energy in wetland surface water generally decreased as surface energy budgets were upscaled temporally. A new method was developed to estimate changes in stored heat energy that overcomes an important data limitation, namely, the limited spatial and temporal availability of water temperature measurements. The new method is instead based on readily available air temperature measurements and relies on the convolution of air temperature changes with a regression‐defined transfer function to estimate changes in water temperature. The convolution‐computed water temperature changes are used with water depths and heat capacity to estimate changes in stored heat energy within the Everglades wetland areas. These results likely can be adapted to other humid subtropical wetlands characterized by open water, saw grass, and rush vegetation type communities.

Water Resources Research↗

USGS1984

Water-level maps of the alluvial aquifer, Northwestern Mississippi, April 1983

Water levels were measured in about 500 wells in the Mississippi River valley alluvial aquifer in northwestern Mississippi during April 1983. Ground-water levels have declined in some areas in recent years as a result of heavy irrigation pumpage from this aquifer. Near the areas of principal recharge, along the major rivers, and near the Bluff Hills, ground-water levels appear to be relatively unaffected by the large aquifer drafts; whereas away from the areas of recharge, in the interior of the basin, ground-water levels have shown a long-term decline. (USGS)

Water-Resources Investigations Report↗